We will perform a double-blind, crossover trial to compare the effects of high-versus low-dose enalapril in patients with chronic congestive heart failure. 40 patients with documented ejection fractions less than 40% who are currently on high-dose ACE inhibitors will be randomized to either high- or low-dose enalapril at the start of the trial. We will measure plasma neurohormone levels, parasympathetic and sympathetic activation as assessed by heart rate variability, and left ventricular systolic and diastolic dimensions determined by surface echocardiography after four weeks. Then the two groups will cross over (high-dose to low-dose and vice versa) and the measurements will be repeated after another four weeks. The two groups will then continue on the same doses of enalapril (started at the crossover) for an additional eight weeks, after which another set of measurements will be obtained. These objective criteria will then be used to compare high- versus low-dose enalapril.